This invention relates to the control of flow in the regenerator chambers of a regenerative combustion furnace. In particular the invention relates to regenerative furnaces in which the combustion chamber communicates with each regenerator by means of a plurality of spaced-apart ports such as the type commonly employed in the melting of glass.
The regenerators used in such furnaces contain a bed of refractory material, such as a stacked arrangement of bricks sometimes called "checker packing," provided with passages for the alternate passing of exhaust gases and combustion air. During the exhaust phase of the combustion cycle, exhaust gases pass through the regenerator bed to heat the packing. In alternate phases of the firing cycle the flow is reversed, and the heat stored in the packing is transferred to combustion air passing through the regenerator to the furnace. The regenerators are generally employed in pairs whereby one regenerator is absorbing heat from the exhaust gas while the other is heating incoming air.
In a conventional, unpartitioned, multiport regenerator, the ports communicate with a common plenum at one side of the regenerator bed, and at the opposite side of the regenerator bed another common plenum communicates with a flue. at one end thereof. The flow of gases to and from the regenerator is by way of the flue, which because of its asymmetrical location has been found to lead to unbalanced gas flows through the regenerator bed. During the exhaust phase of the firing cycle hot exhaust gases from the ports tend to be drawn toward the flue end of the regenerator, and greater quantities of the exhaust gas pass through the packing at the flue end than at the opposite end of the regenerator. Conversely, during the firing phase of the cycle, relatively cool incoming combustion air passing into the regenerator tends to flow to the far end of the regenerator and pass in greater quantities through the packing at that end of the regenerator than at the flue end of the regenerator. As a result, the flue end of the portion of the packing tends to reach higher peak temperatures as well as maintaining higher minimum temperatures over the firing cycle. Because of the high temperatures, the flue end portion of the packing tends to deteriorate faster than others, thereby shortening furnace life and often acting as a restriction on the operation of a furnace. Furthermore, because the stored heat is concentrated in one portion of the packing, the efficiency with which air is preheated during the firing phase is reduced, thereby reducing the overall thermal efficiency of the furnace.
A number of proposals have been made to overcome this problem. An effective and practical solution is disclosed in U.S. Pat. No. 4,375,236 of Yih-Wan Tsai wherein pneumatic jets are employed to alter the flow patterns in a regenerator. In that arrangement, jets in the plenum communicating with the flue are directed in the direction of the flue so as to counter the tendency of excessive amounts of combustion air to travel to the far end of the plenum during the firing phase. During the exhaust phase, the same jets create a low pressure zone that draws additional exhaust gas through the opposite end of the regenerator packing from the flue, thereby countering the tendency to overheat the flue end of the packing. Similarly, a jet may be used in the other plenum communicating with the ports to control the flow dynamics in the regenerator in the manner taught in U.S. Pat. No. 4,375,235 of Yih-Wan Tsai. In the latter arrangement, the jet or jets are situated near the flue end of the plenum and are directed toward the opposite end of the regenerator.
A somewhat different aspect of regenerator flow control is treated in U.S. patent application Ser. No. 510,807 filed July 5, 1983 by Edward P. Savolskis entitled "Port Wall Air Jet for Controlling Combustion Air," and U.S. patent application Ser. No. 510,808 filed July 5, 1983 by Yih-Wan Tsai entitled "Target Wall Air Jet for Controlling Combustion Air." The concepts in these applications involve jets associated with the ports, and although they may be employed to alter flow patterns in the regenerators to some extent, their primary purpose is to control flow through the ports and, in particular, to adjust the distribution of flows among the ports.
The use of pneumatic jets to control flows in regenerators and ports is highly advantageous because of the relatively low cost and the ease with which they may be installed on existing furnaces. Also, the jets can be readily installed without disruption to operating furnaces. The operating expense of providing compressed air to the jets is usually outweighed by the savings in fuel and the cost benefits of extending regenerator life, but it would be desirable to lower the operating costs of the jets to make their use even more economically attractive. Accordingly, it is an object of the present invention to reduce the compressed air consumption of pneumatic jet type flow control means in regenerative furnaces.
Another application of gas jets in regenerative furnaces is for the injection of reactants into the exhaust gas stream for treating pollutants. For example, in U.S. Pat. Nos. 4,328,020 and 4,372,770, ammonia is injected by a carrier jet of compressed air into a glass furnace regenerator to reduce nitric oxides. Economizing on compressed air use in this type of process would likewise be advantageous.